Tuesday, April 21, 2020

Jan van Huysum’s Flowers in a Terracotta Vase (1736) is a riot of floral colour, the equal of anything else by the Dutch flower painters of the seventeenth and early eighteenth centuries. But some of it looks decidedly odd. The leaves spilling out from among the bright blooms don’t look at all healthy, or indeed natural: they are more blue than green.

Jan van Huysum, Flowers in a Terracotta Vase (1736).

This is neither by intention nor mistake. Simply, the yellow pigment that Huysum mixed with blue to create his greens has faded. It was a common problem noted even at the time: the English chemist and writer Robert Dossie wrote in his Handmaid to the Arts (1758) that “The greens we are forced at present to compound from blue and yellow are seldom secure from flying or changing.”

Because artists did not then have a particularly vibrant green pigment that approached the colour of fresh vegetation, they often needed to resort to this mixing of primaries. But unless your primary pigments are bright and pure, such a mixture may become a little murky. Among the brightest of yellows were lake colours, meaning that the pigment was made from a water-soluble organic (plant- or animal-based) substance – basically a dye – fixed to the surface of fine particles of a white powder like chalk or ground eggshell. But organic dyes don't last well when exposed to light: the rays break up the colorant molecules, and the colour “flees”. (Even today pigments and dyes that are not colourfast are said to be “fugitive”.)

Technically these yellows were not exactly lakes, but pinks. Yes, it’s confusing: the word “pink” originally referred not to a pale reddish colour but to a class of pigments similar to lakes but made without the need for an alkali in the recipe. In the seventeenth century there were yellow pinks, green pinks, and light rose-coloured pinks. It is only because the last of these stayed in use for the longest that the term today denotes a hue.

The colorant used for yellow pinks was typically an extract of weld, broom or buckthorn berries. But one used these materials – as Huysum discovered – at one’s own risk.

It’s not that artists didn't have alternative, more stable yellows available. But as with any colour, not all yellows are equal. Those that could be made from minerals or inorganic compounds produced artificially might last longer, but some were rather dirty or pale in their tint.

There was, for example, yellow ochre: a yellowish form of the iron oxide mineral that also came in reds and browns. But if ochre today conjures up a brownish earth colour, that’s because yellow ochre was in truth more like that: fine for tawny hair, but not at all the thing for tulips or satin robes.

Then there was Naples yellow, as it was known from the seventeenth century: a pigment of rather variable composition but which was generally made from synthetic compounds of tin, antimony and lead. The ancient Egyptians knew how to combine lead with antimony ore to make a yellow, and in fact a natural mineral form of that compound (lead antimonite) was also used as an artists’ material. It could be found on the volcanic slopes of Mount Vesuvius, which is how it came to be associated with Naples. Other recipes for a yellow of similar appearance specified mixing the oxides of lead and tin. The ingredients weren’t always too clear, actually: when Italian medieval painters refer to giallorino, you can’t be sure if they mean a lead-tin or lead-antimony material, and it is unlikely that the painters recognized much distinction. Before modern chemistry clarified matters from the late eighteenth century, names for pigments might refer to hue regardless of composition or origin, or vice versa. It could all be very confusing, and from a name alone you couldn’t always be sure quite what you were getting – or, for the historian today, quite what a painter of long ago was using or referring to.

The chemise of Jan Vermeer’s The Milkmaid (c.1658-61) is painted with a lead-tin yellow.

In some respects that’s still true now. A tube of modern “Naples yellow” won’t contain lead (rightly shunned for its toxicity) or antimony, but might be a mixture of titanium white and a chromium-based yellow, blended to mimic the colour of the traditional material. There’s no harm in that – on the contrary, the paint is likely to be not only less poisonous but more stable, not to mention cheaper. But examples like this show how wedded artists’ colours are to the traditions from which they emerged. When you’re talking about vermilion, Indian yellow, Vandyke brown, orpiment, the name is part of the allure, hinting at a deep and rich link to the Old Masters.

One thing is for sure: you won’t find the gorgeous orpiment yellow on the modern painter’s palette (unless perhaps they are consciously, and in this case rather hazardously, using archaic materials). It is a deep, golden yellow, finer than Naples and lead-tin yellows. The name simply means “pigment of gold”, and the material goes back to ancient times: the Egyptians made it by grinding up a rare yellow mineral. But at least by the Middle Ages, the dangers of orpiment were well known. The Italian artist Cennino Cennini says in his handbook, written in the late fourteenth century, that it is “really poisonous”, and advises that you should “beware of soiling your mouth with it.” That’s because it contains arsenic: it is the chemical compound arsenic sulphide. (A different form of the same compound, also found as a natural mineral, furnishes the pigment realgar, the only pure orange colour available to painters until the nineteenth century.)

Natural orpiment (arsenic sulphide).

Orpiment was one of those gorgeous but costly pigments imported to Europe from the East, in this case from Asia Minor. (In the early nineteenth century there were also imports from China, so that orpiment was sold in Britain as Chinese Yellow.) Such alluring imports often arrived through the great trading centre of Venice, and orpiment was hard to acquire up in Northern Europe during the Middle Ages and the Renaissance – unless, like the German artist Lucas Cranach, who ran a pharmacy, you had specialist connections to exotic materials. Some orpiment was made not from the natural mineral but artificially by the chemical manipulations of alchemists. This type can be spotted on old paintings today by studying the pigment particles under the microscope: those made artificially tend to be more similar in size and have rounded grains. From the eighteenth century it was common to refer to this artificial orpiment as King’s Yellow. Rembrandt evidently had a supplier of the stuff, which has been identified in his Portrait of a Couple as Isaac and Rebecca (often called The Jewish Bride), painted around 1665.

If Dutch painters wanted a golden yellow like orpiment without the risk of poisoning, the Age of Empire supplied another option. From the seventeenth century, Dutch paintings (including those of Jan Vermeer) begin to feature a pigment known as Indian Yellow, brought from the subcontinent by the trading ships of Holland. It arrived in the form of balls of dirty yellowish-green, although bright and untarnished in the middle, which bore the acrid tang of urine. What could this stuff be? Might it truly be made from urine in some way? Lurid speculation abounded; some said the key ingredient was the urine of snakes or camels, others that it was made from the urine of animals fed on the yellow Indian spice turmeric.

The mystery seemed to be solved in the late nineteenth century, when an Indian investigator making enquiries in Calcutta was directed to a village on the outskirts of the city of Monghyr in Bihar province, allegedly the sole source of the yellow material. Here, he reported, he found that a group of cattle owners would feed their livestock only on mango leaves. They collected the cows’ urine and heated it to precipitate a yellow solid which they pressed and dried into lumps.

The cows (so the story goes) were given no other source of nutrition and so were in poor health. (Mango leaves might also contain mildly toxic substances.) In India such lack of care for cattle was sacrilegious, and legislation effectively banned the production of Indian Yellow from the 1890s.

J. M. W. Turner was one of the nineteenth-century artists who made much use of Indian yellow.

There has been debate about how much of this story is true, but the basic outline seems to stand up – the pigment has a complicated chemical make-up but contains salts of compounds produced from substances in mango leaves when they are metabolized in the kidneys.

While artists were having to rely for brilliant yellows on fugitive plant extracts, deadly arsenic-laden powers and cows’ urine, one might fairly conclude that they would welcome better yellows. So, then, it’s not hard to imagine the excitement of the French chemist Nicolas Louis Vauquelin when at the start of the nineteenth century he found he could make a vibrant yellow material by chemical alteration of a mineral from Siberia called crocoite.

This stuff was itself red – it was popularly called Siberian red lead, since there was truly lead in it. But in 1797 Vauquelin found there was something else too: a metallic element that no one had seen before, and which he named after the Greek word for colour, chrome or chromium.

“Siberian red lead”, a mineral source of chromium.

The name was aptly chosen, because Vauquelin soon discovered that chromium could produce compounds with various bright colours. Crocoite is a natural form of lead chromate, and when Vauquelin reconstituted this compound artificially in the laboratory, he found it could take on a bright yellow form. Depending on exactly how he made it, this material could range from a pale primrose yellow to a deeper hue, all the way through to orange. Vauquelin figured by 1804 that these compounds could be artists’ pigments, and they were being used that way even when the French chemist published his scientific report on them five years later.

The pigment was expensive, and remained so even when deposits of crocoite as a source of chromium were discovered also in France, Scotland and America. Chromium could also supply greens, most notably the pigment that became known as viridian and which was used avidly by the Impressionists and by Paul Cézanne.

The chromium colours play a major role in the explosion of prismatic colour during the nineteenth century – evident not just in Impressionism and its progeny (Neo-Impressionism, Fauvism and the work of van Gogh) but also in the paintings of J. M. W. Turner and the Pre-Raphaelites. After the muted and sometimes downright murky shades of the eighteenth century – think of Joshua Reynolds’ muddy portraits and the brownish foliage of Poussin and Watteau – it was as if the sun had come out and a rainbow arced across the sky. Sunlight itself, the post-Impressionist Georges Seurat declared, held a golden orange-yellow within it.

For their sun-kissed yellows, the Pre-Raphaelites and Impressionists did not need to rely on chromium alone. In 1817 the German chemist Friedrich Stromeyer noticed that zinc smelting produced a by-product with a yellow colour in which he discovered another new metallic element, named after the archaic term for zinc ore, cadmia: he called it cadmium. Two years later, while experimenting on the chemistry of this element, he found that it would combine with sulphur to make a particularly brilliant yellow – or, with some modification to the process, orange. By the mid-century, as zinc smelting expanded and more of the byproduct became available, these materials were offered for sale to artists as cadmium yellow and cadmium orange.

The artificial pigment cadmium yellow.

The cadmium colours have always stayed rather expensive, though. Nothing really beats cadmium red, a variant that went on market only around 1910. But it is typically around twice the price of other comparable reds, and the same goes for cadmium yellow. In that respect things have not changed so much since an artist in the Renaissance had to weigh up the worth of acquiring expensive orpiment as opposed to the drabber but much cheaper Naples yellow.

There’s a lesson in the cadmium pigments that applies to all colours, through all ages: they have often been byproducts of some other chemical process altogether, often discovered serendipitously as chemists and technologists pursue other goals – to make ointments, say, or soap, glass or metals.

It’s no different now. If you buy a tube labeled “Indian Yellow”, you can be sure no mangos or urine went into its making. Chances are, it will contain a yellow pigment that goes by the unromantic name of PY (pigment yellow) 139 – no mineral or metal salt, but a complicated organic molecule, meaning today that it is carbon-based and resembles molecules found in some living organisms. Chemists will say that it is a “derivative of isoindoline”, but the key point is that at its core is a ring of six carbon atoms joined into a so-called benzene ring.

That’s a clue to the true heritage of these modern organic pigments. Pure benzene, as well as other molecules closer still in their shape and structure to those of PY139, was first isolated in the early nineteenth century from a substance called coal tar, the black tarry residue left over from the industrial extraction of natural gas from coal for gas lighting. Coal tar has a pungent smell – think of the traditional coal-tar soap, which contained some disinfectant compounds distilled from coal tar. This is because it is full of molecules with benzene rings at the core, which tend to be aromatic. (Chemists use that word simply to signify that benzene rings are present, irrespective of smell itself.) In the mid-nineteenth century, German chemist August Hofmann, the leading expert on aromatic coal-tar compounds, set his young English student William Perkin the challenge of trying to make the anti-malarial drug quinine from coal-tar extracts. Perkin didn’t succeed, but instead he found he had made a rich purple substance that he called aniline mauve and began to sell as a dye. That was the beginning of the synthetic-dye industry, which gave rise to the modern era of industrial chemistry: by the early twentieth century, dye manufacturers were starting to diversify into pharmaceuticals and then plastics.

This is the world from which PY139 comes, along with a host of other organic pigments that mimic the old traditional colours with safer, cheaper compounds – many of them used also as food colorants, dyes and inks. One of the first offshoots of the aniline dyes was a yellow, simply called aniline yellow and belonging to an important class of colorants called azo dyes; it was sold commercially from 1863. There is a good chance that, when you see yellow plastic products today, they are coloured with azo dyes.

Winsor and Newton’s azo yellow.

It seems a deeply unglamorous way to brighten the world today, compared to the age of King’s Yellow, saffron and Indian Yellow. It could feel that what is saved in the purse is sacrificed in the romance. Maybe so. But artists are typically pragmatic people, as eager for novelty as they are attached to tradition. There has never been a time when they have not avidly seized on new sources of colour as soon as those appear, nor when they have not relied on chemistry to generate them. The collaboration of art and science, craft and commerce, chance and design, is as vibrant as ever.

Friday, April 17, 2020

This is the second of theree essays on colour commissioned for the catalogue of a now-cancelled exhibition on colour at the Musée d’Orsay in Paris.

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In 1954, French artist Yves Klein said that “I believe that in future, people will start painting pictures in one single colour, and nothing else but colour.”

Klein did not wait for the future – he began painting monochromes in the 1940s. But it was only in the late 1950s that he truly found what he was looking for: a blue so glorious, so lustrous and deep, that it spoke for itself, and said all that Klein wanted to express. “Blue is the invisible becoming visible”, he said.

Yves Klein, IKB 79’ (1959).

It is not always easy to interpret Klein’s remarks, but I believe this one is not so hard to fathom. Blue has always spoken to something beyond ourselves: it is a colour that draws us into the void, the infinite sky. “Blue is the typical heavenly colour”, said Wassily Kandinsky – and who would doubt it after seeing the ceiling of the Arena Chapel in Padua, painted by Giotto around 1305, a vault coloured like the last moments of a clear Italian twilight? Some cultures don’t even recognize the sky as having a hue at all, as if to acknowledge that no earthly spectrum can contain it. In the ancient Greek theory of colour, blue was a kind of darkness with just a little light added.

There’s a strong case to be made, then, that shades of midnight have always been the most treasured of artists’ colours. One of the earliest of the complex blue pigments made by chemistry was virtually an ancient industry in itself. The blue-glazed soapstone carvings known now as faience produced in the Middle East were traded throughout Europe by the second millennium BCE. Faience is typically now associated with ancient Egypt, but it was produced in Mesopotamia as long ago as 4500 BC, well before the time of the Pharaohs. It is a kind of glassy blue glaze, made by heating crushed quartz or sand with copper minerals and a small amount of lime or chalk and plant ash. The blue tint comes from copper – it is of the same family as the rich blue copper sulphate crystals of the school chemistry lab, although faience could range from turquoise-green to a deep dusk-blue. These minerals were typically those today called azurite and malachite, both of them forms of the compound copper carbonate. It’s not at all unlikely, although probably impossible to prove, that the manufacture of glass itself from sand and alkaline ash or mineral soda began in experiments with firing faience in a kiln somewhere in Mesopotamia.

Egyptian faience: a statue of Isis and Horus, c. 332-30 BC.

Similar experimentation might have given rise to the discovery of the trademark blue pigment of the Egyptians, simply known as Egyptian blue or frit. The recipe, at any rate, is almost the same: sand, copper ore, and chalk or limestone. But unlike faience glaze, this material is not glassy but crystalline, meaning that the atoms comprising it form orderly arrays rather than a jumble. Producing the pigment requires some artisanal skill: both the composition and the kiln temperature must be just so, attesting to the fact that Egyptian chemists (as we’d call them today) knew their craft – and that the production of colours was seen as an important social task. After all, painting was far from frivolous: mostly it had a religious significance, and the artists were priests.

Azurite and malachite make good pigments in their own right – the first more bluish, the second with a green tint. They just need to be ground and mixed with a liquid binder. In the Middle Ages that was generally egg yolk for painting on wooden panels, and egg white (called glair) for manuscript illumination. Good-quality azurite wasn’t cheap, but there were deposits of the mineral throughout Europe. To the English (who had no local sources) it was German blue; the Germans knew it as mountain blue (Bergblau).

The mineral form of the blue pigment azurite (hydrated copper carbonate).

A cheaper blue was the plant extract indigo, used as a dye since ancient times. Unlike most organic dyes – those extracted from plants and animals – it doesn’t dissolve in water, but can be dried and ground into a powder like a mineral pigment, and then mixed with standard binding agents (such as oils) to make a paint. It give a dark, sometimes purplish blue, sometimes lightened with lead white. The Italian artist Cennino Cennini, writing in the late fourteenth century, described a “sort of sky blue resembling azurite” made this way from “Baghdad indigo”. As the name suggests – the Latin indicum shares the same root as “India” – the main sources for a medieval artist were in the east, although a form of indigo could also be extracted from the woad plant, grown in Europe.

But the artist who could find a patron with deep pockets would be inclined towards a finer blue than any of these. When the Italian traveller Marco Polo reached what is today Afghanistan around 1271, he visited a quarry on the remote headwaters of the Oxus River. “Here there is a high mountain”, he wrote, “out of which the best and finest blue is mined.” The region is now called Badakshan, and the blue stone is lapis lazuli, the source of the pigment ultramarine.

Cennino shows us how deeply ultramarine blue was revered in the Middle Ages, writing that it “is a colour illustrious, beautiful, and most perfect, beyond all other colours; one could not say anything about it, or do anything with it, that its quality would not still surpass” [Cennino Cennini, Il Libro dell’ Arte (The Craftsman’s Handbook) (c.1390), p. 37-8. (Dover, New York, 1960)]. As the name implies, it came from “over the seas” – imported, since around the thirteenth century, at great expense from the Badakshan mines.

Ultramarine was precious not just because it was a rare import, but because it was extremely laborious to make. Lapis lazuli is veined with the most gorgeous deep blue, but grinding it is typically disappointing: it turns greyish because of the impurities in the mineral. Those have to be separated from the blue material, which is done by kneading the powdered mineral with wax and washing the wax in water – the blue pigment flushes out into the water. This has to be done again and again to purify the pigment fully. The finest grades of ultramarine come out first, and the final flushes give only a low-quality, cheaper product, called ultramarine ash. The best ultramarine cost more than its weight in gold in the Middle Ages, and so it was usually used sparingly. To paint an entire ceiling with the colour, as Giotto did in the Arena Chapel, was lavish in the extreme.

Lapis lazuli, the source of ultramarine.

More often the medieval painter would use ultramarine only for the most precious components of a painting. That seems to be the real reason why most altarpieces of this period that depict the Virgin Mary show her with blue robes. For all that art theorists have attempted to explain the symbolic significance of the colour – the hue of humility or virtue, say – it was largely a question of economics. Or, you might say, of making precious materials a devotional offering to God.

But materials make their own demands. When, during the Renaissance in the fifteenth century, artists began to use oils rather than egg yolk to bind their pigments, they found that the switch both enalbed and demanded new techniques. The colours dried more slowly and so could be blended into subtle shadows and highlights, enhancing the realism of the work in line with the emerging humanist philosophy. But the artists also had to cope with the fact that some pigments look different when bound in oils; ultramarine was one of them.

This is largely a matter of physics: light is bent and scattered to different degrees in the two binding agents, and the result is that ultramarine looked more transparent. Painters were then forced to compromise the purity of precious ultramarine by mixing it with a little lead white to keep it strong and opaque. Its mystique waned accordingly, and artists began to feel more free to use a whole range of lighter blues in their works. The art historian Paul Hills says that “Blue by the fifteenth century was moving away from its association with starry night, the vault of the heavens, to the changeful sky of day.”

You can compare azurite and ultramarine side by side in Titian’s explosion of Renaissance colour, Bacchus and Ariadne (1523). Here is that starry vault, indeed turning to day before our eyes, and it is painted in ultramarine. So too is Ariadne’s robe, which dominates the scene. But the sea itself, on which we see Theseus’s boat receding from his abandoned lover, is azurite, with its greenish tint.

Titian’s Bacchus and Ariadne (1523). Ariadne’s robe, and the sky, are painted in ultramarine.

Over the centuries, artists accumulated a few other blues too. Around 1704 a colour-maker named Johann Jacob Diesbach, working in the Berlin laboratory of alchemist Johann Conrad Dippel, was attemtping to make a red lake pigment when he found that he had produced something quite different: a deep blue material. He had used a batch of the alkali potash in his recipe, supplied by Dippel – but which was contaminated with animal oil allegedly prepared from blood. The iron used by Diesbach reacted with the material in the oil to make a compound that – unusually for iron – is blue in colour. By 1710 it was being made as an artist’s material, generally known as Prussian blue.

It wasn’t entirely clear what had gone into this mixture, and so for some years the recipe for making Prussian blue was surrounded by confusion and secrecy. In 1762 one French chemist declared that “Nothing is perhaps more peculiar than the process by which one obtains Prussian blue, and in must be owned that, if chance had not taken a hand, a profound theory would be necessary to invent it.” But chance was a constant companion in the history of making colours. At any rate, Prussian blue was both attractive and cheap – a tenth of the cost of ultramatine – and it was popular with artists including Thomas Gainsborough and Antoine Watteau. It comprises some of the rich blue Venetian skies of Canaletto.

Another blue from the Renaissance and Baroque periods went by the name of smalt, which is not so very different from the cobalt-blue glass of Gothic cathedrals such as Chartres, ground to a powder. Its origins are obscure, but may well come out of glass-making technology; one source attributes the invention to a Bohemian glassmaker of the mid-sixteenth century, although in fact smalt appears in earlier paintings. Cobalt minerals were found in silver mines, where their alleged toxicity (actually cobalt is only poisonous in high doses, and trace amounts are essential for human health) saw them named after “kobolds”, goblin-like creatures said to haunt these subterranean realms and torment miners. Natural cobalt ores such as smaltite were used since antiquity to give glass a rich blue colour, and smalt was produced simply by grinding it up – not too finely, because then the blue becomes too pale as more light is scattered by the particles. As a result of its coarse grains, smalt was a gritty material and not easy to use.

Some art historians make no distinctions between this “cobalt blue” and those that were given the name in the nineteenth century. But the latter were much finer, richer pigments, made artificially by systematic chemistry. In the late eighteenth century the French government asked the renowned chemist Louis-Jacques Thénard to look for a synthetic substitute for expensive ultramarine. After consulting potters, who used a cobalt-tinted glassy blue glaze, in 1802 Thénard devised a strongly coloured pigment with a similar chemical constitution: technically, the compound cobalt aluminate. Cobalt yielded several other colours besides deep blue. In the 1850s a cobalt-based yellow pigment called aureolin became available in France, followed soon after by a purple pigment called cobalt violet – the first ever pure purple pigment apart from a few rather unstable plant extracts. A sky blue pigment called cerulean blue, a compound of cobalt and tin, was a favourite of some of the post-Impressionists.

The water in Renoir’s Boating on the Seine (La Yole) (c.1879) is painted in cobalt blue.

But what artists craved most of all was ultramarine itself – if only it wasn’t so expensive. Even by the mid-nineteenth century it remained costly, which is why the Pre-Raphaelite Dante Gabriel Rossetti caused much dismay (not to mention added expense) when he upset a big pot of ultramarine paint while working on a mural for Oxford University.

By Rossetti’s time, however, artists did at last have an alternative – it’s just that several of them had not yet learnt to trust it. As chemical knowledge and prowess burgeoned in the early nineteenth century, bringing new pigments such as cobalt blue onto the market, it seemed within the realms of possibility to try to make ultramarine artificially.

It was a prize well worth striving for, because pigment manufacture had become big business. The manufacture of colours and paints wasn’t supplying artists; there was now a taste for colour in the world at large, in particular for interior decoration. Factories were set up in the nineteenth century to make and grind pigments. Some sold them in pure form to the artist’s suppliers, who would then mix up paints for their customers from pigment and oil. But some pigment manufacturers, such as Reeves and Winsor & Newton in England, began to provide oil paints ready-made; from the 1840s these were sold in collapsible tin tubes, which could be sealed to prevent paints from drying out and could be conveniently carried for painting out of doors.

Mindful of the importance of the pigment market, in 1824 the French Society for Encouragement of National Industry offered a prize for the first practical synthesis of ultramarine. It is a complicated compound to make – unusually for such inorganic pigments, the blue colour comes not from a metal but from the presence of the element sulphur in the mineral crystals. This composition of ultramarine was first deduced by two French chemists in 1806, offering clues about what needed to go into a recipe for making it. In 1828, an industrial chemist named Jean-Baptiste Guimet in Toulouse described a way to make the blue material from clay, soda, charcoal, sand and sulphur, and he was awarded the prize (despite a rival claim from Germany). In England this synthetic ultramarine was subsequently widely known as French ultramarine, and Guimet was able to sell it at a tenth of the cost of the natural pigment. By the 1830s there were factories making synthetic ultramartine throughout Europe.

Artists looked upon this substitute with considerable caution, however. Ultramarine still retained some of its old mystique and majesty, and painters were reluctant to believe that it could be turned out on an industrial scale. Perhaps the synthetic variety was inferior – might it fade or discolour? Actually synthetic ultramarine is (unlike some synthetic pigments) very stable and reliable, but J. M. W. Turner was evidently still wary of it when, in the mid-century, he was about to help himself to the ultramarine on another artist’s palette during one of the “finishing days” at the Royal Academy, where artists put their final touches topaintings already hung for display on the walls. Hearing the cry that this ultramarine was “French”, Turner declined to dab into it.

But by the end of the century, synthetic ultramarine was a standard ingredient of the palette: small wonder, given that it could be a hundred or even a thousand times cheaper than the natural variety. Synthetic ultramarine is the pigment in Yves Klein’s patented International Klein Blue, which he used for a series of monochrome paintings in the 1950s. But ultramarine never looked like this before – at least, not on the canvas.

Klein noticed that pigments tend to look richer and more gorgeous as a dry powder than when mixed with a binder – another consequence of how light gets transmitted and refracted – and he sought to capture this appearance in a paint. In 1955 he found his answer in a synthetic fixative resin called Rhodopas M60A, made by the Rhone-Poulenc chemicals company, which could be thinned to act as a binder without impairing the chromatic strength of the pigment. This gave the paint surface a matt, velvety texture. Klein collaborated with Edouard Adam, a Parisian chemical manufacturer and retailer of artists’ materials, to develop a recipe for binding ultramarine in this resin, mixed with other solvents.

Yves Klein, Venus Bleue (1962).

Even in the modern era, then, some artists were still depending on chemical assistance and expertise. Despite the profusion of new pigments with complicated and recondite chemical formulations, the intimate relationship of painters to their materials has not been entirely severed.

Thursday, April 16, 2020

This is the first of three essays on colours that were to be included in the catalogue for an exhibition at the Musé d'Orsay in Paris this year, which has been cancelled. So I'm putting them here for your delectation. Each essay focuses on the pigments developed and used through time for one of the primary colours.

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One hundred thousand years ago, the last Ice Age covered much of northern Europe with glaciers several kilometres thick. Small groups of Homo sapiens coexisted with other, now extinct human ancestors: Neanderthals and Denisovans. Life was nasty, brutish and short. Yet in a cave in what is today South Africa, humans found the time and inclination to mix red paint.

Their tools have been found in Blombos Cave on the Southern Cape coast: grindstones and hammer-stones for crushing the pigment, and abalone shells for mixing the powder with animal fat and urine to make a paint that would be used to decorate bodies, animal skins and perhaps cave walls. The red colour was made from ochre, a natural, soft, iron-rich mineral chemically similar to rust.

A piece of engraved ochre from Blombos cave in South Africa.

The evolution of complex ways of thinking and socializing seems only to have happened fifty thousand years later – and yet even at the dawn of human culture it seems that the urge to adorn our surroundings and ourselves with colour was deeply felt. It was done in the colours of nature: black charcoal, white chalk and ground bone, and the brownish-red of ochre. It’s no wonder that a word for “red” seems to be one of the earliest colour words to appear in languages across the globe, after those for black and white. The cave paintings made 15-35 millennia ago in Chauvet, Lascaux and Altamira attest to the genuine artistry that early humans achieved.

Red ochre is still on the artist’s palette today: a “dirty” red, some might say, but an honest, humble one, and cheap too. It’s iron that gives the mineral this hue. Like many metals when chemically combined with other elements, it absorbs light within a characteristic band of the visible spectrum, soaking up the blues and greens but reflecting the reds. That red is purer in the colour of blood, where an iron atom sits at the heart of the protein haemoglobin and ferries oxygen around our bodies. The bloody hue is reflected in the technical name for ochre-like minerals: haematite, literally “blood-stone”, which is iron oxide.

During the Industrial Revolution, chemists perfected a method for making iron oxide artificially, so that the red colour could be more precisely controlled. It was an offshoot of the manufacture of sulphuric acid, an important ingredient for textile bleaching. This red substance was sold to artists as “Mars red”, an echo of the old alchemical term for iron compounds. The planet Mars was long associated with redness. It has that hue even to the naked eye, for its surface is covered with iron oxide minerals.

But the classic red pigments of the artists don’t rely on iron minerals, the hue of which is not the glorious red of a sunset, or indeed of blood, but of the earth. For many centuries, the primary red of the palette came from the compounds of two other metals: lead and mercury.

Lead is something of a chameleon metal. By combining the raw metal with various other substances – vinegar, carbon dioxide, air – alchemists and artisans knew since the time of the ancient Egyptians how to obtain white, yellow and red materials. Red lead was the finest of these colours, made by heating “white lead” in air. It was known too in ancient China from at least the fifth century BCE. Roman and Greek painters used it, although the Roman writer Pliny in the first century AD was wary of artists who used bright colours like this too lavishly – the sober artist, he insisted, deployed a more muted palette, with reds of ochre.

To Pliny, any bright red was called minium, and red lead was a slightly second-rate version: minium secundarium. But by the Middle Ages minium had become more or less synonymous with red lead, which was used extensively in manuscript illumination. That art came to be described by the Latin verb miniare, “to paint in minium”, from which we get the term “miniature”: nothing to do, then, with the Latin minimus, “smallest”. The association today with a diminutive scale comes simply from the constraints of fitting a miniature on the page.

A miniature painted in red lead from c.1300.

Pliny’s best minium was a different red pigment, called cinnabar. This was a natural mineral: chemically, mercury sulphide. It was mined in the ancient world, partly for use as a red colorant but also because the liquid metal mercury could easily be extracted from it by heating. Mercury was thought to have almost miraculous properties: ancient Chinese alchemists in particular used it in medicines.

By the Middle Ages, alchemists and craftspeople knew how to make mercury sulphide artificially by combining liquid mercury and yellow, pungent sulphur (available naturally in mineral form) in a sealed vessel and heating them. This process, which was described in a craftsman’s manual of around 1122 by the German monk Theophilus, can give a finer quality of red pigment. It was a procedure of great interest to alchemists too, as the Arabic scholars of the eighth and ninth centuries had claimed that mercury and sulphur were the basic ingredients of all metals – so that combining them might be a route to making gold. Theophilus, however, had no such esoteric arts in mind; he just wanted a good red paint.

“Artificial cinnabar” became known by the name vermilion. The etymology is curious, and shows the confusing and treacherous flux of colour terms in an age when the hue of a substance seemed more significant than vague, pre-scientific notions of what its chemical identity was. It stems from the Latin vermiculum (“little worm”), since a bright red was once extracted from a species of crushed insect: not a paint pigment but a translucent dye of scarlet colour, arising from an organic (carbon-based) substance that the insects produce. Such dyes were also known as kermes, the etymological root of “crimson”. Because the insects that made it could be found on Mediterranean trees as clusters encrusted in a resin and resembling berries, the dyes might also be called granum, meaning grain. From this comes the term “ingrained”, implying a cloth dyed in grain: the dye was tenacious and did not wash out easily.

Vermilion is used abundantly in Masaccio’s Saints Jerome and John the Baptist (c.1428-9), in the National Gallery, London.

Vermilion is by no means the only close link between the reds of textile dyes and the reds of paint pigments. The former are translucent and dissolve in water, and are generally organic substances extracted from animals or plants – such as cochineal, an extract of New World beetles that became popular with cloth dyers in the sixteenth century. But paint pigments must be opaque and long-lasting, whereas dyes tended to fade as they were washed out or as sunlight broke down the delicate organic molecules.

Red dyes were associated with majesty, opulence, status and importance: they were the colours used for cardinals’ robes in the Middle Ages and Renaissance. Painters needed fine reds to render on board and canvas these dignitaries whose portraits they were increasingly commissioned to paint. Red lead and vermilion served well enough in the Middle Ages, but the increased demand for verisimilitude in the Renaissance highlighted the difference between the orange hue of the pigments and the crimson of the dyes.

One way to capture the quasi-purple magnificence of those dyes was to fix the colorant molecules onto solid, colourless particles that could be dried and mixed with oils like a regular pigment. This process involved some challenging chemistry, but even the ancient Egyptians knew how to do it. The basic idea is to precipitate a fine-grained white solid within a solution of the dye: the dye sticks to the particles, which dry to make a dark red powder. In the Middle Ages this process used the mineral alum, which can be converted to insoluble white aluminium hydroxide. The pigment made this way was called a lake, after the word (lac or lack) for a red resin exuded by insects indigenous to India and southeast Asia.

One of the best red lakes of the late Middle Ages and the Renaissance was made from the dye extracted from the root of the madder plant. As lake manufacture was perfected, artists such as Titan and Tintoretto began to use these pigments mixed with oils, giving a slightly translucent paint that they would apply in many layers for a deep wine-red tint or would wash over a blue to make purple. In this as in much else we can see the constant exchange in materials and knowhow between dyers and pigment-makers.

There is abundant, rich red lake in Titian’s Portrait of the Vendramin Family (1543-7).

A popular source of a luxurious, blood-red lakes in the late Middle Ages was the dye called cochineal, harvested in eastern Europe from a species of beetle that encrusted the perennial knawel plant with a resinous crust. The colour comes from organic compounds made by the insects themselves, which are killed, dried and crushed. According to one estimate, about 70,000 insects were needed to make one pound of this so-called carmine lake. The plant was harvested around midsummer, and if the crop failed, the price of carmine soared. After the discovery of the New World, however, cochineal for dyes and pigments gained a more reliable (if scarcely cheaper) source as an import from the Spanish colonies in the Americas.

The existence of strong red pigments was vital to the evolution of the palette. According to the art historian Daniel Thompson, the invention of a method to make synthetic vermilion transformed the nature of medieval art:
“No other scientific invention has had so great and lasting an effect upon painting practice as the invention of this colour… Given abundant vermilion, the standard of intensity in the painter’s palette automatically rises. Equally brilliant blues and greens and yellows were required to go with it… If the Middle Ages had not had this brilliant red, they could hardly have developed the standards of colouring which they upheld; and there would have been less use for the inventions of the other brilliant colours which came on the scene in and after the twelfth century.” (D. V. Thompson, The Materials and Techniques of Medieval Painting, p.106. Dover, New York, 1956.)

Aside from the creation of red lakes, rather little about the painter’s reds changed from the Middle Ages until modern times. The Impressionists in the late nineteenth century made avid use of the new yellows, oranges, greens, purples and blues that advances in chemistry had given them, yet their reds were not really any different to those of Raphael and Titian.

It wasn’t until the early twentieth century that a vibrant and reliable new red entered the repertoire. The discovery of the metal cadmium in 1817 immediately produced new yellow and orange pigments, but a deep red was made from this element only around the 1890s. The yellow and orange are both cadmium sulphide; but to get a red, some of the sulphur in this compound is replaced by the related element selenium. It wasn’t until 1910 that cadmium red became widely available as a commercial colour, and its production became more economical when the chemicals company Bayer modified the method in 1919.

Cadmium red is a rich, warm colour – it is arguably the painter’s favourite red, except for the price. That was certainly true for Henri Matisse, for who red held a special valence - as his interiors in La Desserte (aka The Red Room, 1908), Red Studio (1911) and Large Red Interior (1948) attest. Of the second of these, art critic John Russell said “It is a crucial moment in the history of painting: colour is on top, and making the most of it.”

Matisse’s The Red Studio (1911) is painted in cadmium red.

Colour is on top. That was that way in went in the twentieth century, from the strident chromatic statements of the Fauves (Matisse at their head) to the stark primaries of Ellsworth Kelly and the hypnotic maroon colour fields of Mark Rothko (whose experiments with new reds made from synthetic and fugitive dyes did not end well). Colour went from being the artist’s medium to being the subject. In that shifting of the agenda, red led the way.